20

Here is a picture of what I intend to use:

Enter image description here

I believe (and could be wrong about this) that over time as the structure is moved, the nut that was fastened to hold the structure together will gradually loosen. Is there way to make the nut so tight and fixed that it will never become loose automatically, but only when the user needs to open it?

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  • 9
    Clarify please; do you plan on the fastener being easily removed regularly with hand tools? Or is it acceptable to make it permanent and require destructive removal ?
    – Criggie
    Jan 22 at 11:50
  • 4
    If we knew what the structure was, and was made of, we may well come up with better fixings than nuts/bolts.
    – Tim
    Jan 22 at 15:34
  • 3
    Note, the OP's use case is here. Also, it's highly unlikely that anything more than a pair of washers and a good, firm snug on the wrenches is necessary to keep this particular assembly "tight enough". Unless you're moving the desk on a regular basis, that's all you're going to need. This won't just fall apart on its own - there are no inherent vibrations as there might be for bolts on a car.
    – FreeMan
    Jan 23 at 16:22
  • OK, the bolt will keep together two panels of chipwood, where one is put on top of the other and bolted togeher. Then the panels are connect vertically in a desk so their face is facing wall. When can bolts loose overtime, I am not sure.
    – quantum231
    Jan 23 at 22:51
  • 1
    @quantum231 I've noted several follow-up questions on several of the answers. While I fully understand that you're a beginner and you need to learn (learning is GOOD), you're seriously overthinking this! Have any of the bolts on the original desk come loose while the desk was just simply sitting there? If you're moving it all the time, then yeah, it could be a problem, but for 99.999% of us, a desk, once assembled, just sits there and desks. Bolts don't just come loose on their own on stationary objects. Moving objects like cars, dishwashers, etc. are a different story.
    – FreeMan
    Jan 25 at 13:24

15 Answers 15

14

instead of (or with) a regular washer:

enter image description here

you can use these tension ones:

enter image description here enter image description here

then there is also one with a rubber side:

enter image description here

as for a nut already suggested:

enter image description here

or two regular ones and lock the first one with the second:

enter image description here

or hardlock nuts:

enter image description here

of course the best (one time) securing is to weld bolt and nut:

enter image description here

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  • 2
    This is the most comprehensive answer but everyone has provided valuable input. I hope page will help people in the future.
    – quantum231
    Jan 24 at 21:22
32

The easiest way is to replace the nut with a Nylanut AKA Nyloc nut: enter image description here By Original uploader was Btarski at en.wikipedia. - Originally from en.wikipedia; description page is/was here., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5047606

These provide resistance such that it will not (easily) unscrew unless you use a wrench/socket to remove it.

You could also use a lock washer between the nut and the washer.

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    Or Threadlocker, or... Red threadlocker (not great for wooden things joined - the blowtorch needed to convince it to let go might scorch the wood a bit..
    – Ecnerwal
    Jan 22 at 1:04
  • 2
    Good answer, but use a tool kind of imply's a special tool, instead of a little bit more force with common wrenches/ratchets.
    – crip659
    Jan 22 at 1:13
  • 1
    @crip659 I agree and made an edit.
    – DoxyLover
    Jan 22 at 1:43
  • 8
    Another option is to use locking nuts - have two nuts - tighten once as normal and then tighten the second while holding the first. This is the old way of doing it :-) Jan 22 at 3:40
  • 7
    Remember nylock nuts are supposed to be single use only. Subsequent reuse has a lower resistance so they come off easier. Enough reuse, and the grip degrades down to that of a plain nut.
    – Criggie
    Jan 22 at 11:52
30

Thread Lock Adhesive

You can use a thread locking compound, such as this. enter image description here

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  • 11
    Welcome to the site - good first answer. You might want to call out the different "strengths" of thread locker, like "hand tool" vs "heat release"
    – Criggie
    Jan 22 at 18:31
  • 2
    Note that thread locker doesn't work on all metals. There are primers available that are basically copper oxide suspended in a solvent that remedy this. Thread locker also takes (generally) 24 hours to cure at room temperature. It's a good idea to spend 5 min reading the manufacturer's instructions before using it.
    – J'e
    Jan 23 at 15:39
  • I'm confused! I always though blue Locktite could be loosened with tools, while the red required heat, yet this package seems to indicate that the red can be removed with "hand tools".
    – FreeMan
    Jan 23 at 16:19
  • 6
    @FreeMan, welcome to the world of Loctite, where the (standard) blue threadlocker comes in a red bottle and the (high strength) red threadlocker comes in a blue bottle. {facepalm} Jan 23 at 16:40
  • ummm... What. The. Heck??? (Funny story: I've got a bit of thread locker in my toolbox. It came with something I had to assemble and it's a blue liquid in a white bottle. May or may not be Loctite™ brand...)
    – FreeMan
    Jan 23 at 16:49
25

You can also find bolts with a locking nylon patch applied, like these from Nylok: enter image description here

These are useful if the bolt is going into a blind threaded hole.

Added The Following

As I said in a comment below, these are considered superior to even locking adhesives in that chance of an assembler applying the wrong amount of locking compound is eliminated.

For our hi-rel applications, there's a specified process that's followed when using these, and similar fasteners, which include the following:

  1. The bolt is torqued to the proper setting, using a calibrated torque wrench. There are always two operators involved, one to do the tightening and another to witness that the proper torque was used.
  2. Depending on the application, we may apply a dab of structural adhesive to the head of the bolt to further ensure that it won't back out.
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  • 1
    Wasn't aware of those; thanks for the tip!
    – keshlam
    Jan 22 at 4:19
  • Nylok nuts have been around for a very long time - are these new in comparison?
    – Tim
    Jan 22 at 10:59
  • @Tim - I don't know when those nylon patch fasteners first showed up. We've been using them for at least 20 years or longer in the aerospace industry.
    – SteveSh
    Jan 22 at 13:22
  • Depends so much on the usage...for safety critical usage the nylon is probably better, but for normal home use the adhesive is way more practical. The adhesive is more flexible--you don't have to plan ahead, just use it with whatever you've already got. Especially helpful if you tend to modify or repair existing things that come with hardware. And the actual hardware is reusable, if you bolt everything together and then need to open it up again you're only out a tiny bit of adhesive. Jan 23 at 16:01
  • Wait, this is a nylok bolt instead of nut? Who knew? This is awesome info, thanks!
    – FreeMan
    Jan 23 at 16:18
19

Lock Nut / Double Nutting

If there's enough thread exposed through the joint, then you can fit two nuts. The first nut is tightened to the required torque for your application, and the second nut is then tightened against the first nut, to a higher torque value.

Traditionally the locknut has been thinner than the main nut, but it is possible to just use two of the same nut.

Example - the locknut may have a larger diameter than the original nut, or it may be the same.
enter image description here

There is some debate about whether the thin locknut should be on first (as pictured) or the correct way where the main nut takes the load and the thinner lock nut goes on last.

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  • 2
    This site recommends the thin nut coming first, as in the picture boltscience.com/pages/twonuts.htm
    – Bobby J
    Jan 22 at 16:57
  • 5
    @BobbyJ yeah there's three schools of thought, and valid points for all of them. And if one's better than another, its a very small difference. If your application depends on that difference, then the fastener is under-specced so upsize the biolts.
    – Criggie
    Jan 23 at 2:31
  • 3
    Those are typically called "jam nuts" IME.
    – Huesmann
    Jan 23 at 12:12
  • 1
    you mean a pinch nut!
    – Turbo
    Jan 23 at 21:05
  • 2
    @quantum231 they don't need to be different thicknesses
    – Chris H
    Jan 24 at 10:28
17

To round out the smorgasbord a bit:

Drill a hole through the nut and bolt when tight, insert a cotter pin.

Or drill a hole only through the bolt and use a castellated nut. Actually two holes at right angles allows finer adjustments (1/12 of a turn rather than 1/6th of a turn to line up one of the holes with the slots in the castle-nut)

Or use safety wire after drilling the hole. https://en.wikipedia.org/wiki/Safety_wire

4
  • This works only when there's enough room to get a drill plus bit in close enough to get the hole something like parallel to the object/s being bolted together.
    – Tim
    Jan 22 at 11:01
  • 2
    Safety wiring nuts used to be standard practice in the aerospace industry. For the most part, that has been replaced with the nylon (or some other substance) locking patch I showed. These are considered superior to even locking adhesives in that chance of applying the wrong amount of locking compound is eliminated.
    – SteveSh
    Jan 22 at 13:03
  • When I worked one summer as a machinist's helper building heavy mechanical cranes for unloading container ships, we did this. Sometimes we would have the nut welded in place instead. It depended on the specs.
    – Wastrel
    Jan 22 at 14:32
  • 1
    As it happens, today I was attending a criminal prosecution involving a split pin in a castellated nut on a heavy mechanical crane. Something about the pin not being correctly placed and the resulting accident....
    – david
    Jan 23 at 7:54
9

Flange washer

This solution requires modification to the bolt, in the form of a channel or slot running up one side.

Then a washer with a tab/flat is slid on before the nut, something like this:

enter image description here

Once assembled and torqued down, the washer is deformed around at least one side of the nut, by using leverage often from a large flathead screwdriver/crowbar and hammer.

This mechanism is common on car wheel bearings. Here's a photo from an old landrover. In this example, the washer is sandwiched between two nuts and one segment of the washer has been folded back (away from camera) and another sector is about to be folded forward around the visible front nut.

enter image description here

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  • 1
    Had never heard of this method - very interesting, thanks.
    – Armand
    Jan 22 at 16:02
  • 1
    Land Rover Defender? Jan 22 at 19:20
  • 1
    Wheel bearings I've worked with had a hole in the spindle and a special nut that was used along with a cotter pin to prevent the bolts from backing out, after it had been torqued down correctly to pre-load the bearings.
    – SteveSh
    Jan 23 at 15:11
  • 1
    Yup, this is a technique used on more than a few axle nuts, even on newer cars. My VW has a different technique, though: 105 ft/lbs then turn an additional 180°. Stretches the bolt, locks the threads, makes the bolt a 1-time use.
    – FreeMan
    Jan 23 at 16:22
  • 1
    @quantum231 vibrations (that's the main culprit of bolt loosening) as a byproduct of high RPM. because even "balanced" wheels from a car are just balanced to be "good enough" and not "totally perfect". and even if they would be, then even the smallest rock/pebble can unbalance them and introduce a shockwave of vibrations
    – servant0
    Jan 24 at 21:35
9

Lockwashers like these can be useful in some applications.lockwashers

6
  • These would be "crinkle washers" to me - other areas will likely have different names.
    – Criggie
    Jan 22 at 18:28
  • 1
    You might choose to include split washers and nordlock washers here too, as a retention system under the nut.
    – Criggie
    Jan 22 at 18:30
  • 2
    @Criggie - they are star / lock washers to me. Crinkle washers are different, they are literally a very thin flat washer that is crinkled to provide some force when a nut is fastened down on-top, rather than cutting into the surface, like the ones pictured.
    – SiHa
    Jan 23 at 8:36
  • 1
    IME, these don't really work, and people tend to over tighten them so they break/fail. Jan 23 at 16:43
  • Does such washers exist for bolts or just small screws? I have seen these type of washers when I was passing by in shop once upon a time, I did wonder what they could be used for.
    – quantum231
    Jan 23 at 22:57
7

Torque the bolt properly.

This preloads the bolt up to some percentage of the breaking load. Under normal use the clamping preload should be greater than the dynamic load the bolt sees.

As a consequence of the clamping force being larger than the preload, it will not deform elastically during use, and then nut will not work loose under most conditions.

5
  • Bang on. I'll just add that if the torque setting isn't known for the assembly, then hand-tighten and then use a (torque-)wrench to turn the nut tighter through 90 degrees. This suppresses fatigue-inducing dynamic loads.
    – Trunk
    Jan 23 at 12:05
  • 1
    Or you can look up standard values for the bolt you're using. For instance a M8 10.9 zinc plated? 29 Nm. This is a good enough value if nothing is specified.
    – vidarlo
    Jan 23 at 12:22
  • yes, certainly this is the most useful answer, i.e pre-empt the loosening of the bolt.
    – quantum231
    Jan 23 at 23:00
  • @vidarlo the OP is bolting together veneered chipboard. You'd need big washers to spread the load and avoid crushing the veneer
    – Chris H
    Jan 24 at 11:17
  • 1
    @ChrisH That's not mentioned in the question. A comment by someone else claims this. As the question stands this (and other answers) are perfectly valid.
    – vidarlo
    Jan 24 at 11:52
6

Another, way more permanent plan is to have the bolt about one thread's worth protruding out of the nut. It may well involve cutting said bolt. Then peen the extra thread over, and the two will never work apart.

If the structure needs to be moved frequently then perhaps a different fixing would do a better job. Pop rivets, welding, for example.

4

Lockwasher, locking nut as shown above, threadlocker blue (the removable kind) (choose all three)

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  • 2
    This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review
    – gnicko
    Jan 22 at 4:11
  • 6
    @gnicko Suggesting 3 ways to solve the issue seems like an answer to me; could you clarify?
    – Armand
    Jan 22 at 4:46
  • 4
    @Armand probably cos its short and lacking in detail, and was posted after a couple of other longer answers covering similar points.
    – Criggie
    Jan 22 at 12:16
  • 3
    This has the beginnings of a good answer with the threadlock suggestion, but as written it's just a series of brief comments on other answers that came before it.
    – gnicko
    Jan 22 at 19:45
  • 3
    @gnicko: Agreed it's not a very good answer, especially not mentioning what "threadlocker blue" is. But it is an answer. And it was better than nothing before other answers with more detail were posted, since "threadlocker blue" and the others are searchable terms. It's low enough quality that it didn't deter people from mentioning the same things in their own answers. Unless this stack is very strict about not answering in comments, though, this is the kind of thing that I'd have posted as a comment. But posted as an answer, I'd say it is an answer, just not worth an upvote. Jan 23 at 5:30
4

Depending on the application, you can tack weld the nut to the bolt. Of course this weakens the nut and bolt, and you'll need a torch or grinder if you ever want to remove it, but I have seen this technique successfully used many a time.

1
  • 4
    I've seen this used to secure remote farm gates, to keep trespassing 4WD drivers out of private land and prevent them lifting a gate off the hinges. A small portable and self-container welder is invaluable on the farm.
    – Criggie
    Jan 23 at 2:35
4

Aircraft used safety wire through the nut/bolt for critical applications. ( May have changed in the many years since I saw them.)

5
  • 1
    Probably too hardcore
    – DKNguyen
    Jan 23 at 2:14
  • Goodness yes, I remember doing this as an apprentice.
    – RedSonja
    Jan 23 at 7:24
  • 1
    Not only aircraft. It's used in industry in general where positive locking is required. It also makes inspection very easy, which has a benefit in some industries. If wire is undamaged, bolt is OK.
    – vidarlo
    Jan 23 at 8:54
  • But you have to check that the wire is running the right way - to tighten, not to loosen. Don't ask how I know that.
    – RedSonja
    Jan 23 at 11:45
  • 1
    Also safety wire requires a fixed point to tie the other end to, often another bolt if there's one close enough. These are definitely still in use in modern industrial/military installations, but the place they're installed generally has to be designed to use them. Jan 23 at 19:22
2

The most important thing to do is to ensure that, in the final assembly, there is no rotational degree of freedom around the axis of the bolt.

For example, I have a number of cooking pans where a single bolt holds the handle to the pan. They all repeatedly come loose and require re-tightening, because the handle can rotate slightly back and forth around the axis of the bolt. But the same can happen in arrays of multiple bolts, e.g. corners of a rectangle where sides are independent pieces, where the positions of the bolts aren't held rigidly relative to one another, allowing them all to rotate back and forth. No matter what you've done to try to prevent loosening, bolts that act as pivot points will always loosen.

To solve this, you need to have enough bolts, in the right places, to rigidly constrain the whole assembly against this. At that point, you can think about other measures to eliminate loosening from vibrations and other smaller-order effects.

2
  • 1
    Pans are also subject to heat-cycling which will back out threaded fasteners over time no matter what. The best fix is having the cooking base and handle cast from the same metal at the same time then adding a heat-resistant covering to the handle.
    – Criggie
    Jan 24 at 23:22
  • 1
    @Criggie: I'm skeptical of that claim, in the absence of rotational motion. I don't experience that with properly torqued threads in 3D printer hotend. But even if it does happen, that's one of the smaller-order effects I was talking about mitigating with other measures. The dominant problem is the rotational degree of freedom. Jan 25 at 5:17
1

Linseed Oil

If you are working on odd-jobs and have an average garage at your disposal, linseed oil congeals to a rubber consistency (See info about polymerization of linseed oil) .

enter image description here

1
  • 1
    This is the old-school way of thread locking. Bicycle wheels use "spoke prep" which was originally linseed oil on initial assembly, allowing smooth tightening of spoke nipples while truing the wheel, which cured after some time and resisted future drift/movement without completely eliminating it.
    – Criggie
    Jan 24 at 23:19

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